Wireless problem! Please help!!!

Hello! I installed BackTrack 5 R1 32 bit on my laptop Acer Aspire 5750G but I cant connect to my wireless network. When I open Wicd Network Manager, it says "No wireless networks found". When I open terminal and write iwconfig, it shows:

lo no wireless extension.

eth0 no wireless extension.

When I write ifconfig wlan0 up, ti says:
wlan0: ERROR while getting interface flags: No such device


Please help!!!

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